What I've learned from this and other sites is:

(BO) Bovine Overy

Positives: Fast. Works well. Relatively safe.

Negatives:

+Can work too well and too fast for some guys.
+Changes are PERMANENT.
+Has a 'memory effect'  and can continue to make body changes well after use has stopped. no telling what those changes might be until they have happened, either.
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(PM) Pueraria Mirifica

Pros:

Slow acting. Can make adjustments, just slow or stop taking it.  Changes made will reverse in time.

Cons: Can get expensive because it is so slow acting. Can also get very frustrating to use.

and which is safer?  Depends on what the user wants, I guess.


K.

I would say that's it in a very short nutshell. 

Granted their are risks that may vary from individual to individual for both PM and bo, but there's no way to tell before starting. For example some users of PM had developed blood clots. 

But again in a very short summary I feel that is correct.

Ultimately, In my opinion no one can say that either is safer!
Anything you put into your body has some risk, I'm highly allergic to kiwi fruit of all things!
The important thing is to do your research in full, then decide what you feel is best for you and start off slow and more than anything else - listen to your body.

Good luck

(PM) Pueraria Mirifica

Pros:

Slow acting. Can make adjustments, just slow or stop taking it.  Changes made will reverse in time.

Cons: Can get expensive because it is so slow acting. Can also get very frustrating to use.

Once you bud and start to develop breast tissue, those changes from PM will be permanent. Be sure this is what you really desire.